The following background discussion is not an admission that anything discussed below is citable as prior art or common general knowledge.
High efficiency reverse osmosis processes (“HERO”; see, for example, U.S. Pat. Nos. 5,925,255 and 6,537,456) can achieve higher water recovery rates compared to conventional reverse osmosis processes. HERO relies on a series of pretreatment steps prior to reverse osmosis filtration, which includes use of weak acid cation resin columns, degasification and pH adjustment.
Other processes may involve the use of microfiltration, ultrafiltration, ion exchange and chemical precipitation to achieve greater water recovery (see, for example, U.S. Pat. Nos. 5,501,798, 6,113,797 and 6,461,514).